This invention relates to novel substances which can be extracted from cereals, novel extraction procedures, and the use of the products as therapeutic agents, biocompatible films and as additives in food and cosmetics.
xcex2-Glucan polysaccharides present in cereals comprise D-glycopyranosyl units. The units are linked together by (1xe2x86x923) or (1xe2x86x924) xcex2-linkages, xcex2-Glucans of this type comprise up to approximately 15% of the solids in oats and barley cereals. They typically have a molecular weight of around 2.5 million.
xcex2-Glucans are useful as soluble dietary fibre. Soluble fibre remains undigested except by colonic microflora in the lower intestines. This enhances the growth of bacteria beneficial to health. Soluble dietary fibre is believed to have a role in the prevention of certain diseases including colonic cancer and diseases associated with high serum cholesterol levels. Soluble fibre can be used for the treatment and prevention of constipation, for the improvement of bowel regularity, and for the regulation of the glycaemic response associated with the digestion of many substances.
xcex2-Glucans are considered to have hypocholesterolemic activity. xcex2-Glucans are also useful as food ingredients. They have neutral flavours and provide bulk in addition to having desirable mouthfeel and texture characteristics. In this context, xcex2-glucans are known as fat replacements in some foods.
The reported methods of extracting xcex2-glucans from cereal involve a number of steps. First, the milled cereal is treated to deactivate enzymes associated with the cereal. Then the xcex2-glucan is extracted from the cereal into warm water after which the solids are removed from the solution.
Large quantities of water-miscible organic solvents are added to the solution to precipitate the xcex2-glucan, generally along with other polysaccharides. The xcex2-glucan is of low purity and of generally high molecular weight. It is also known to carry out the enzyme deactivation step after the water extraction rather than as a first step. The deactivation step inhibits hydrolysis of the xcex2-glucan thereby maintaining a high average molecular weight of the xcex2-glucan.
Aqueous solutions of the xcex2-glucan obtained via the known methods have minimal functionality with respect to temperature. They are generally high molecular weight gums and form viscous aqueous solutions although they do not dissolve in water easily.
The xcex2-glucans obtained by the reported methods can contain arabinoxylans and starch. These impurities can be responsible for the formation of viscous aqueous solutions during extraction which are difficult to process. Gummy or tacky solids can result when the solids are recovered as a dry product. These products are difficult to redissolve, even at high temperatures.
The known methods of recovering xcex2-glucan from the aqueous solution include precipitation of the xcex2-glucan by the addition of a water miscible organic solvent (such as ethanol) followed by filtration, and spray- or freeze-drying of the precipitate.
The extraction procedures suggested by the prior art have limited commercial potential in view of the number of steps and hence the cost involved.
It is an object of this invention to provide a xcex2-glucan product and a simple and effective method of extracting xcex2-glucan, or to at least provide the public with a useful alternative.
In a first aspect of this invention there is provided a process for obtaining xcex2-glucan, having a lower average molecular weight than in its native state, from cereal comprising:
mixing the cereal with water to form a slurry of an aqueous solution of xcex2-glucan and a solid residue such that the xcex2-glucan is partially hydrolysed by one or more enzymes associated with the cereal to give xcex2-glucan having a lower average molecular weight than in its native state,
separating the aqueous solution from the solid residue, and
recovering the xcex2-glucan from the aqueous solution,
wherein there is there is no step of deactivation of the one or more enzymes during the process.
In accordance with a second aspect of this invention there is provided a process for recovering xcex2-glucan from an aqueous solution of xcex2-glucan comprising:
freezing the solution,
thawing the solution to give a precipitate in water, and
separating the precipitate from the water,
wherein the major non-aqueous component of the precipitate is xcex2-glucan.
The invention provides a xcex2-glucan produced by any of the processes of the first and second aspects of the invention.
The invention also provides a xcex2-glucan extracted from cereal which forms a gel when dissolved in heated water and then allowed to cool.
In accordance with a further feature of the invention there is provided a composition containing xcex2-glucan for use as a hypocholesterolemic agent. A composition containing xcex2-glucan is also provided for use in treating or preventing constipation, for regulating bowel activity, or for regulating glycaemic response.
The invention also provides a method of treating hypercholesterolemia in a patient in need comprising administering to the patient an effective amount of xcex2-glucan.
The invention further provides a method of treating or preventing constipation, a method of regulating bowel activity and a method of regulating glycaemic response, each method comprising administering to a patient in need an effective amount of xcex2-glucan.
The invention provides the use of a xcex2-glucan as a food ingredient, as an additive in cosmetic compositions, as a film forming agent in wound dressings and in food coatings, as a matrix for the slow release of an agent carried in the matrix, and for the modification of the properties of other polysaccharides.
The invention also provides an animal feed consisting of cereal from which xcex2-glucan has been extracted to a substantial extent. The invention further provides a cereal for use in brewing processes wherein xcex2-glucan has been extracted from the cereal.
The cereal used in this invention may be any xcex2-glucan containing grain or plant material including, but not limited to, barley, oats, rice, rye, triticale, maize and wheat. The preferred cereal is barley. In addition, waxy cereals have the advantage over non-waxy cereals that less leeching of amylose from the starch granules into the extraction solution occurs.
The physical properties of xcex2-glucans depend largely on their average molecular weight. The expression xe2x80x9chigh molecular weight xcex2-glucanxe2x80x9d as used herein means xcex2-glucan having an average molecular weight substantially similar to the average molecular weight of xcex2-glucan found in the cereal (typically 2xc3x97106 to 3xc3x97106). The expression xe2x80x9clow molecular weight xcex2-glucanxe2x80x9d as used herein means xcex2-glucan having a lower average molecular weight (5xc3x97103 to 1.5xc3x97106) relative to the average molecular weight of xcex2-glucan found in the cereal.
The average molecular weight of the xcex2-glucan extracted from the cereal is a function of the amount of time the xcex2-glucan is in contact with one or mole hydrolase enzymes associated with the cereal. Thus, when the cereal is mixed with water, the one or more hydrolase enzymes are believed to become activated with respect to reaction with the xcex2-glucan. A portion of the xcex2-glucan molecules are hydrolysed to smaller units leading to xcex2-glucan recovered from the extraction process having low molecular weight.
The hydrolase enzymes associated with the cereal include enzymes endogenous to the cereal and also enzymes present in, or produced by, microorganisms which may have adhered to the cereal.
The average molecular weight of xcex2-glucan obtained by aqueous extraction of cereal, without deactivation of hydrolase enzymes, can be controlled by controlling the time of the extraction. In the process of the first aspect of the invention cereal is mixed with water to form a slurry so that xcex2-glucan is extracted from the cereal into solution. The longer the extraction time, the greater the amount of hydrolysis of the xcex2-glucan. Therefore, a low molecular weight xcex2-glucan can be obtained if no deactivation of the enzymes occurs. Additionally, xcex2-glucan of predetermined average molecular weight can be obtained by predetermining the extraction time.
The cereal may be extracted with water at any temperature in the range 0-80xc2x0 C., preferably 30-70xc2x0 C., or more preferably 45-60xc2x0 C. At temperatures above approximately 80xc2x0 C., the enzymes associated with the cereal are thought to become deactivated.
It will be appreciated that the yield of xcex2-glucan recovered from the cereal varies with water temperature during the extraction process. A higher temperature generally gives a higher yield.
The cereal may be mixed with water adjusted to a pH in the range 1-10, preferably 5-8.
In addition to controlling the average molecular weight of the xcex2-glucan by controlling the extraction time, the partial hydrolysis of the xcex2-glucan is anticipated to be assisted by the addition of exogenous xcex2-glucan hydrolysing enzymes to the mixture or by the addition of acid of the mixture.
It is also anticipated that treatment of the aqueous mixture with an arabinoxylan degrading enzyme, such as xylanase, or a starch degrading enzyme, such as an amylase, will lead to a xcex2-glucan product of improved purity.
Cooling the aqueous solution of xcex2-glucan to a temperature between approximately 0xc2x0 C. and 10xc2x0 C. may lead to formation of a gel.
Any of the known processes for recovering xcex2-glucan from an aqueous solution or the process of the second aspect of this invention may be employed to recover the low molecular weight xcex2-glucan.
The cereal, which may be in the form of whole grain, bran, pollard, flour or other powder milled to a desired particulate size, may be stirred with water at approximately 50xc2x0 C. until a desired amount of xcex2-glucan is extracted into solution, for example, up to 48 hours, preferably up to 10 hours, more preferably up to 3 hours. The aqueous phase may then be separated from any remaining solid matter by centrifugation followed by decanting or filtration. The xcex2-glucan present in the aqueous solution is then recovered preferably by the process of the second aspect of this invention.
The average molecular weight of the low molecular weight xcex2-glucan recovered may be in the range up to 1,500,000, preferably up to 600,000, more preferably up to 300,000, for example, 5,000 to 50,000. It will be appreciated that the average molecular weight of the xcex2-glucan recovered may vary from cereal to cereal and may vary depending on the form of the cereal. Hence, some experimentation may be required in order to predetermine the average molecular weight of the product for a given mixing time.
The process of the second aspect of the invention relates to the recovery of xcex2-glucan from an aqueous solution of xcex2-glucan by freeze-thawing the solution.
In this process, the aqueous solution can be formed by the process of the first aspect of this invention or by any of the known methods which result in a low molecular weight xcex2-glucan product. The known methods generally require deactivation of the enzymes present in the cereal prior to the aqueous extraction of xcex2-glucan. The xcex2-glucan is then partially hydrolysed enzymatically or by treatment with acid to give low molecular weight xcex2-glucan.
The aqueous solution is frozen at a temperature below 0xc2x0 C., preferably at a temperature between approximately xe2x88x9220xc2x0 C. and xe2x88x9210xc2x0 C. It does not appear to be important how long the solution is kept frozen. The frozen solution is then allowed to thaw, preferably by standing at room temperature (15-25xc2x0 C.).
The xcex2-glucan product is recovered as a whitish solid particulate, gelatinous or stringy material which has precipitated out of solution. This is separated by filtration or other means from the aqueous phase and is essentially insoluble in cold water. The xcex2-glucan product is then dried. Drying can be assisted by freezing the precipitate and then allowing it to thaw. This process removes further water from the solid material.
The precipitate may be dried by any known means including air drying, pressing, washing with an alcohol, heating or freeze drying.
The resultant xcex2-glucan product has been found to be of high purity, generally 70% by weight of the total solids or greater. Redissolving the xcex2-glucan containing product in water followed by repeating the freezing and thawing steps, provides a xcex2-glucan product of higher purity for example, greater than 90%.
While the process provides a xcex2-glucan product of high purity, it is anticipated that the use of an arabinoxylan degrading enzyme, such as a xylanase, and/or a starch degrading enzyme, such as an amylase, will improve the purity of the xcex2-glucan by making it easier to remove undesired arabinoxylans and starch as readily soluble oligosaccharides. The degrading enzyme may be used prior to the freezing and thawing steps of the xcex2-glucan product recovered following the freezing and thawing steps, may be redissolved in water and treated with one or more such degrading enzymes.
The xcex2-glucans so isolated have novel functional properties. Products obtained by known processes form viscous solutions that have little or no structure over a temperature range of 0 to 100xc2x0 C. The xcex2-glucan produced by the present invention forms free-flowing solutions that can develop considerable structure. Gels may form at temperatures below approximately 60xc2x0 C. and concentrations above about 0.5% w/w, preferably above 1% w/w.
A viscous fluid is a fluid which shows resistance to flow. Mobile liquids like water have low viscosity but liquids which flow with difficulty, such as treacle, have high viscosity.
The term xe2x80x9cgelxe2x80x9d as used herein is defined as a partially coagulated solid in which a liquid is dispersed. Gels are generally semirigid but easily deformed. Gums are soluble in water to give viscous solutions but do not coagulate to form gels.
In a preferred embodiment of the invention, there is provided a xcex2-glucan product which forms a soft gel at a concentration above about 0.5% w/w.
Preferably, the xcex2-glucan product is dissolved when the water is heated to above approximately 60xc2x0 C. A gel forms when the solution cools.
Generally, xcex2-glucan of lower molecular weight forms gels rapidly. For example, a 30,000 molecular weight xcex2-glucan may begin to solidify after approximately 15 minutes whereas a 400,000 molecular weight xcex2-glucan may take approximately two hours to form a gel. Of these xcex2-glucans, those of higher molecular weight typically form stiffer gels.
Another feature of the invention is the use of the low molecular weight xcex2-glucan to modify the properties of other polysaccharides, for example, other high molecular weight xcex2-glucans.
The xcex2-glucan product of this invention may be used as an hypocholesterolemic agent. It is also useful for treating or preventing constipation and for the regulation of bowel activity. In addition, the xcex2-glucan product may be used to regulate the glycaemic response, i.e. increased blood sugar levels, following the digestion of certain foods.
The therapeutic agents of the invention can be prepared in composition form to be taken as tablets, capsules, solutions, suspensions or other type of composition. These compositions can be formed by any known method.
The low molecular weight xcex2-glucan of the invention can be utilised for purposes other than as an hypocholesterolemic agent. The unique functional properties will have a variety of uses particularly in processed food products. It is preferred in accordance with the invention to simply add the xcex2-glucan to food products. Because the xcex2-glucans are natural food components, it is believed the consumer resistance to modified or unnatural food additives will not be prevalent.
One quality of the low molecular weight xcex2-glucans of the invention is that they have a good mouth feel. This makes them suitable as a fat mimetic in food products. Their ability to form films which are edible makes them potentially useful as food coatings, for example, glazings. The film forming properties of xcex2-glucans also enable them to be useful as films for wound dressings. xcex2-Glucans appear to inhibit the formation of ice crystals in frozen foods. They are therefore useful in frozen foods where a smooth mouthfeel is desired, for example, ice cream.
Additionally, the pores in the solid structure of the gelled or dried xcex2-glucan product of this invention are anticipated to enable the xcex2-glucans to be used as slow release agents for pharmaceuticals and for flavours, for example, in foods.
Cereals containing xcex2-glucan are used as stock feed, particularly as poultry or pig feed. They will not be as effective as a nutrient in view of the anti-nutrient activity of the xcex2-glucans. By extracting the xcex2-glucans, the remaining solid material will have increased value as an animal feed. This will particularly be the case with barley.
The invention further provides an animal feed containing cereals from which the xcex2-glucan has been removed by a process involving solubilising the xcex2-glucans into an aqueous solution and removing the solid material as the animal feed. The solid material may also be used in brewing processes to reduce problems such as clogged fillers caused by the precipitation of xcex2-glucans from solution during processing. Typically at least 30% of the xcex2-glucan has been removed from the cereal. Preferably, at least 50% has been removed. More preferably, at least 80% of the xcex2-glucan has been removed.
The following examples illustrate the invention but are not to be construed as limiting: